Apparatus for producing a nonwoven fabric from continuous filaments is already known from German Patent 17 85 158 and British Patents 1,282,176 and 1,297,582. In such apparatus, a tow of filaments is drawn from a liquefied composition from spinnerets with the aid of a gaseous propellant, and the individual filaments are laid down on an apron, in the form of a belt, to form the nonwoven.
A significant characteristic in terms of the quality of nonwovens is their uniformity and strength; the strength, defined as the ratios of the strengths in the longitudinal direction and in the transverse direction, is determined substantially by the angle at which the individual filaments are laid down--that is, the delivery direction with respect to the production direction.
It is already conventional to use spinning beams (or die manifolds) with a multiplicity of individual draw-off tubes for the filaments, with one separator associated with each draw-off tube. The task of the separator is to separate the filaments from the propellant air and at the same time to spread apart the filament bundle. This spreading at the same time defines the delivery angle. When separators are used, allowance must be made in practice for the fact that the various separators have a major influence on one another, because of the emerging propellant air. Accordingly, there is only one favorable setting for the separators, and it can be selected only once, and thus necessarily defines the delivery direction. Hence there only a very limited opportunity exists for attaining different delivery angles.
If a slight change in the angular position of the various separators should in fact be desirable, in order to enable different delivery angles, then the entire apparatus must first be shut off, because changes of this kind cannot be done during ongoing operation of a system. Moreover, changing the delivery angle is associated with considerable amounts of rejection in the nonwoven fabric produced.
It has also already been proposed to provide two spinning beams, with separators spaced apart from one another in the production direction, and with each spinning beam having its own delivery direction for the filaments. The result is so-called crosswise delivery, with two respectively predetermined delivery angles.
As noted above, the various separators affect one another because of the emerging propellant air, so that work can only be done with one favorable setting of the separators that is to be selected once, so that the delivery direction is necessarily predetermined. Thus in this version having two spinning beams, still only limited delivery directions in crosswise delivery can be attained. Moreover, to change the delivery angle, the entire apparatus must first be shut off, with the attendant disadvantages already mentioned.
A need exists in the industry for different strengths in different directions, depending on the intended use of the nonwoven, and this need cannot be met with the previously proposed version having two spinning beams.
In another apparatus for producing a nonwoven fabric from continuous filaments, the so-called curtain method has also already been used. This method dispenses with the many drawoff tubes mentioned above; nor is any spreader (separators) used. The tow, which forms a curtain of large surface area, extends at right angles to the production direction; that is, the preferential delivery direction is parallel to the production direction.
Because of the speed of the filaments, which here is higher in every case relative to the speed of the delivery belt, the delivered filaments move in a serpentine or wavy pattern. In certain regions, individual filaments come to be stacked one on the other.
Although a nonwoven fabric produced with such an apparatus does have a preferred strength in the longitudinal direction, that is, in the production direction, its strength in the transverse direction is extremely poor.